The woman usually is not aware of the loss, specifically when there is no vaginal bleeding or abdominal pain. A missed abortion is usually diagnosed when the blood hCG fails to increase as expected, on ultrasound when there is either no embryo (blighted ovum), when there is an embryo or fetus but no heartbeat. Most miscarriages which eventually have symptoms such as bleeding or passage of tissue, usually begin with a missed abortion. The embryo or fetus has died several weeks before there are symptoms and the bleeding begins. The difference between a miscarriage that begins with bleeding and a missed abortion is that the missed abortion was diagnosed by ultrasound or a blood test and before there is bleeding or other symptoms.